Former hedge fund trader Danielle Chiesi, a lead figure in the Galleon Group insider trading case, pleaded guilty today to three counts of conspiracy to commit securities fraud — marking a major victory for federal prosecutors in their widespread insider trading probe.

The 45-year-old faces up to 15 years in prison for her crimes, although her plea deal with prosecutors recommends a much lighter sentence of 37 to 46 months.

“I am deeply ashamed of what I did by crossing the line…I ruined a 20-year career in my field,” Chiesi told Manhattan federal court judge Richard Holwell this afternoon. “I didn’t trade on the stocks personally, but I knew what I was doing was wrong.”

The former high school beauty queen admitted to sharing confidential information with her co-defendant, Galleon founder Raj Rajaratnam, the feds’ top target, and her former boss Mark Kurland, with whom she was romantically involved.

She also confessed to obtaining confidential information from another romantic interest, formerIBM exec Robert Moffat on stocks including IBM, Advanced Micro Devices and Sun Microsystems.

Chiesi’s plea paves the way for Manhattan US Attorney Preet Bharara, whose office is prosecuting the case, to checkmate Rajaratnam, the last remaining defendant in the two-year-old affair.

Rajaratnam, who has pleaded guilty and remains free on bail, is set to go to trial at the end of February.

Prosecutors say Chiesi’s former employer, hedge fund New Castle, pocketed $1.7 million in ill-gotten gains on her tips.

Speaking in a calm, clear voice, Chiesi suggested the case has been taking on toll on her health, saying she’s been seeing a psychiatrist and taking anti-anxiety drug Zymbalta. Chiesi appeared to have lost a lot of weight since her October 2009 arrest.

She showed signs of tearing up only when she apologized to her family, who she thanked for supporting her. She was frequently accompanied to court last year by her mother.

Chiesi, who was caught on government wiretaps cursing with cohorts over getting good inside information and about her concerns over getting caught, arrived at the courthouse arm-in-arm with two young nieces. She also was accompanied by her sister and her well-coifed mother.

Chiesi’s lawyer, Alan Kaufman, said she is not cooperating with prosecutors and that “she is hopeful that by acknowledging what she did do and what she did not do, she can move on with her life and that her privacy and her family’s privacy will be respected.”

Chiesi and Rajaratnam were among a group of six people whose high-profile arrests in October 2009 broke word of a insider-trading probe that would come to ensnare as many as 27 hedge fund traders and corporate executives.

Of the original six arrested that day, only Rajaratnam has not pleaded guilty. The others, including Chiesi’s former boss, Mark Kurland, and Rajaratnam pal and Intel exec Rajiv Goel, all copped pleas.

In one example of insider trading, during a July 2008 telephone call intercepted by the FBI, after talking with an executive at Akamai Technologies, Chiesi told Rajaratnam, “I’m trading it tomorrow…They’re gonna ‘guide’ down. I just got a call from my guy.”

Chiesi instructed Rajaratnam to “just keep shorting every day,” a strategy that helped her hedge fund New Castle profit when the news about the company’s earnings were made official.

Late last year, Bharara’s office scored another major victory when Judge Holwell ruled the controversial wiretaps the FBI collected during its probe could be used in trials against Rajaratnam and Chiesi.

In an interview with Reuters last year, Chiesi defended her innocence and said she and her co-defendant Rajaratnam were going to fight it to the end. “There is not even a chance we will do one day in jail. We didn’t do anything wrong,” Chiesi said at the time.

Ever mindful of her appearance, Chiesi, after her court appearance today, steeled herself before leaving the courthouse to face a phalanx of photographers. Before pushing through the courthouse door, she took time to re-apply some lip gloss — and then she was gone.